The present invention relates to hydraulic lash adjusters, and more particularly, to such lash adjusters which define internal fluid reservoirs, and which operate in engagement with the surface of another member such as a rocker arm, or a pushtube, wherein the area of engagement between the lash adjuster and the other member requires lubrication.
Hydraulic lash adjusters (also sometimes referred to as "lifters") for internal combustion engines have been in use for many years, to eliminate clearance (or lash) between engine valve train components under varying operating conditions, in order to maintain efficiency and to reduce noise and wear in the valve train. A hydraulic lash adjuster (HLA) operates on the principle of transmitting the energy of the valve actuating cam through hydraulic fluid, trapped in a pressure chamber under a plunger. During each operation of the cam, as the length of the valve actuating components varies as a result of temperature changes and wear, small quantities of hydraulic fluid are permitted to enter the pressure chamber, or escape therefrom, thus effecting an adjustment in the position of the plunger, and consequently adjusting the effective total length of the valve train.
In a typical, prior art HLA, there is a body defining a bore and a plunger assembly disposed within the bore to define a pressure chamber. The plunger defines a low pressure chamber (or reservoir) which receives fluid from an external source, such as an oil passage in the cylinder head. The plunger also includes either a "ball plunger" portion, or a "pushrod socket" portion which, by way of example only, engages a mating surface of a rocker arm or a pushtube, respectively. In a Type V valve gear, the pushrod socket moves with the plunger assembly and, therefore, subsequent references hereinafter and in the appended claims to a "ball plunger" will be understood to mean and include the pushrod socket used in the Type V lash adjuster. The engagement of the ball plunger and the rocker arm requires lubrication, and lubrication fluid flows from the reservoir of the HLA, through a metering valve (metering pin) to the external surface of the ball plunger. The metering valve must be able to meter or control the flow of fluid from the reservoir, and at the same time, prevent air from entering the reservoir through the metering orifice whenever the fluid pressure in the reservoir drops. It is because of this later requirement that a simple orifice in the ball plunger is not acceptable.
An attempt of those skilled in the prior art to meet the requirements set forth above is illustrated and described in U.S. Pat. No. 4,004,558 in which the metering orifice is defined by a diametral clearance between a bore in the ball plunger and the metering pin. However, the metering orifice is typically quite small, and as is well known to those skilled in the art, maintaining accurate control of an area which is a diametral clearance is quite difficult.
German Patent DE 19507240 illustrates another attempted solution in which the ball plunger defines a bore receiving a rivet. The rivet shank defines an axial groove which would appear functionally capable of serving as the metering orifice. However, the rivet is fixed within the bore and would likely become plugged up with dirt and other contaminants, thus preventing the necessary flow of lubrication fluid.